In the LTE (Long Term Evolution) system specified in the 3GPP (3rd Generation Partnership Project), in uplink, SC-FDMA (Single-Carrier Frequency Division Multiple Access) is adopted which achieves low Peak-to-Average Power Ratio (PAPR) and is effective in increasing the coverage. Accordingly, by scheduling in a radio base station apparatus, basically, radio resources of some frequency and time are allocated to one mobile terminal apparatus (UE: User Equipment), and users in the same cell are orthogonal in the frequency and time domains. However, in the LTE system, since the system is based on one-cell frequency reuse, interference from adjacent cells is high, and particularly, the interference level from the UE present at the cell edge is high. Therefore, measures against inter-cell interference are required to compensate for such adjacent-cell interference and maintain certain reception quality.
As the measures against inter-cell interference, the role performed by transmission power control in uplink is significant, and the radio base station apparatus is required to control transmission power of the mobile terminal apparatus to meet predetermined reception quality, while considering pass loss between the user and the radio base station apparatus and interference imposed on adjacent cells. In the LTE system, fractional transmission power control is adopted as the transmission power control method in consideration of inter-cell interference.
Transmission power of signals (PUSCH (Physical Uplink Shared Channel), PUCCH (Physical Uplink Control Channel), SRS (Sounding Reference Signal)) transmitted in uplink in the LTE system is controlled by a combination of open-loop control by parameters that the radio base station apparatus notifies at relatively long intervals and pass loss measured by the mobile terminal apparatus and closed-loop control by TPC commands that the radio base station apparatus notifies at relatively short intervals based on communication status (for example, reception SINR (Signal to Interference plus Noise Ratio) in the radio base station apparatus) between the radio base station apparatus and the mobile terminal apparatus. More specifically, the transmission power of the PUSCH is given by following equation (1) (Non-patent Document 1).PPUSCH(i)=min{PMAX,10 log10(MPUSCH(i))+P0—PUSCH(j)+α·PL+ΔTF(i)+f(i)}  Eq. (1)
This fractional transmission power control enables inter-cell interference to be reduced by setting target reception power corresponding to pass loss PL of the mobile terminal apparatus (which is achieved by parameter α of open-loop control).
FIG. 25 is a diagram to explain fractional transmission power control. In FIG. 25, the vertical axis represents target reception power (PO—PUSCH), and the horizontal axis represents pass loss (PL). In fractional transmission power control, for the purpose of suppressing inter-cell interference, transmission power is set so as to decrease target reception power of a mobile terminal apparatus present at a cell edge. In other words, since it is considered that the user exists at the cell edge when pass loss (PL) is large and that the user exists near the radio base station apparatus when pass loss is small, the target reception power of the mobile terminal apparatus of the user near the radio base station apparatus is relatively increased, and the target reception power of the mobile terminal apparatus of the user at the cell edge is relatively decreased. The gradient of the primary characteristic line of such a relationship is −(1−α).
Further, as inter-cell interference measurements in uplink, both signalings (signaling via X2 interface between radio base station apparatuses) of “UL Overload Indication (OI)” and “UL High Interference Indication (HII)” are defined in the LTE system (Non-patent Document 2). As shown in FIG. 26, ULOI is used for a radio base station apparatus (adjacent cell) of a high reception interference level to notify an adjacent radio base station apparatus (communicating cell) of the interference level. For example, the radio base station of the cell receiving ULOI performs control for reducing transmission power at the cell edge. Meanwhile, when a mobile terminal apparatus under control is positioned at the cell edge, ULHII is used for the radio base station apparatus to beforehand notify the radio base station apparatus of the adjacent cell of resource block (RB) information allocated to the mobile terminal apparatus. The radio base station apparatus of the adjacent cell receiving the ULHII executes control for performing frequency scheduling to avoid the RBs.